Add a handler for enabled/disabling assist.

chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java

Index: chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
diff --git a/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java b/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
index 4d7f29bcc236d03f5ad8256594400875b7c45070..1e6fe13b49554c0f4bc62348cf8cc8c780296d81 100644
--- a/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
+++ b/chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java
@@ -4,6 +4,7 @@
 
 package org.chromium.chrome.browser;
 
+import android.app.Activity;
 import android.app.ActivityManager;
 import android.app.SearchManager;
 import android.content.Context;
@@ -172,6 +173,22 @@ public class ChromeTabbedActivity extends ChromeActivity implements ActionBarDel
     // Time at which an intent was received and handled.
     private long mIntentHandlingTimeMs = 0;
 
+    private class TabbedAssistStatusHandler extends AssistStatusHandler {
+        public TabbedAssistStatusHandler(Activity activity) {
+            super(activity);
+        }
+
+        @Override
+        public boolean isAssistSupported() {
+            // If we are in the tab switcher and any incognito tabs are present, disable assist.
+            if (isInOverviewMode() && mTabModelSelectorImpl != null
+                    && mTabModelSelectorImpl.getModel(true).getCount() > 0) {
+                return false;
+            }
+            return super.isAssistSupported();
+        }
+    }
+
     @Override
     public void initializeCompositor() {
         try {
@@ -346,6 +363,11 @@ public class ChromeTabbedActivity extends ChromeActivity implements ActionBarDel
         return (ChromeTabCreator) tabCreator;
     }
 
+    @Override
+    protected AssistStatusHandler createAssistStatusHandler() {
+        return new TabbedAssistStatusHandler(this);
+    }
+
     private void handleDebugIntent(Intent intent) {
         if (ACTION_CLOSE_TABS.equals(intent.getAction())) {
             getTabModelSelector().closeAllTabs();
@@ -1264,7 +1286,7 @@ public class ChromeTabbedActivity extends ChromeActivity implements ActionBarDel
 
     @Override
     public boolean isInOverviewMode() {
-        return mLayoutManager.overviewVisible();
+        return mLayoutManager != null && mLayoutManager.overviewVisible();
     }
 
     @Override
@@ -1273,22 +1295,25 @@ public class ChromeTabbedActivity extends ChromeActivity implements ActionBarDel
     }
 
     @Override
-    public void onOverviewModeStartedShowing(boolean showToolbar) {
-        if (mFindToolbarManager != null) mFindToolbarManager.hideToolbar();
-    }
-
-    @Override
     public void onSceneChange(Layout layout) {
         super.onSceneChange(layout);
         if (!layout.shouldDisplayContentOverlay()) mTabModelSelectorImpl.onTabsViewShown();
     }
 
     @Override
-    public void onOverviewModeFinishedShowing() { }
+    public void onOverviewModeStartedShowing(boolean showToolbar) {
+        if (mFindToolbarManager != null) mFindToolbarManager.hideToolbar();
+        if (getAssistStatusHandler() != null) getAssistStatusHandler().updateAssistState();
+    }
+
+    @Override
+    public void onOverviewModeFinishedShowing() {}
 
     @Override
     public void onOverviewModeStartedHiding(boolean showToolbar, boolean delayAnimation) {}
 
     @Override
-    public void onOverviewModeFinishedHiding() {}
+    public void onOverviewModeFinishedHiding() {
+        if (getAssistStatusHandler() != null) getAssistStatusHandler().updateAssistState();
+    }
 }